Compressor Cycles On And Off

We had a question recently about why an air compressor cycles on and off?  What might be the reasons?

In order to nail down the cause of this we need to better understand what the questioner means when they say the compressor cycles on and off?

Does it mean that they use air from the tank and the compressor starts to refill the tank?

Does this mean that the pressure in the tank reaches the normal cut out pressure, the compressor stops, and when no compressed air is used from the tank, the pressure in the tanks drops anyway and the compressor restarts?

Or do they mean that while the compressor pump is filling the tank back up to the normal cut out pressure level, the pump cycles on and off while it is trying to fill the tank?

If their concern is this –  they use air from the tank and the compressor starts to refill the tank – this is typically normal, and as long as the pressure in the tank is dropping through air use to the regular cut in pressure setting, the compressor starts, air is pumped into the tank, and the tank pressure reaches the normal cut out and the pump starts, this is how they are supposed to work.

If the symptom is thisno compressed air is used from the tank, the pressure in the tanks drops anyway and the compressor restarts – that suggests a leak. Since the air is trapped in the tank via a check valve, and if there is no hose plugged into the compressor coupler, there are few areas on the compressor that could leak.

Compressed air regulator - www.fix-my-compressor.com

Air should not be coming from anywhere on the compressor regulator is there is no hose plugged into the compressor coupler.

You could check with soap and water all the fittings on the compressor to see if one is leaking. Splash soap and water around the regulator too. If the diaphragm inside the regulator has failed, air could be leaking through the diaphragm and out the relief port. No air should be coming from the regulator at all if no air line is plugged into the compressor coupler.

If the problem is thisthe pump cycles on and off while it is trying to fill the tank – that’s a bit more complex fix.  Causes could be:

  • problem with power supply to compressor
  • compressor on/off switch is failing
  • pressure switch failing and cycling before it should
  • run capacitor on motor failing
  • centrifugal switch on motor shaft failing
  • motor windings failing

With a multi-meter monitor the power supply to the compressor  to be sure it is not fluctuating. Typically this will not be the cause.

With the compressor switch turned on, measure to ensure that power supply through the switch is constant. It would be unusual if an on/off switch were causing cycling power, but check it just to be sure.

With the multi-meter monitor the output from the pressure switch to the motor circuit while the compressor is running. Obviously much care must be taken to ensure safety, as live wires are involved. If the power running from the pressure switch to the motor circuit is constant while the compressor is filling, that lets the pressure switch out as the cause. If output from the pressure switch to the motor circuit is cycling along with the compressor going on and off, then the pressure switch is the problem and it needs to be replaced.

If it is not the power supply that causes the compressor to cycle on and off, then that leads us to the capacitors, or the motor itself.

Other pages on this site provide information on testing the capacitors.

If it is the motor that turns out to be the case, it’s time (unless you are really handy) to take the compressor motor to a shop for a thorough test and repair.

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